> *Also, let's remember that a significant portion of human
> repetitive DNA, namely the Alu repeats, code for the 7SL RNA that is a
> component of signal recognition particle. Not all "complex" repetitive
> DNA is retrotransposon or other selfish DNA, or "mysterious" in some way.
I may well be mistaken, but I think it is incorrect to say that the
Alu element IS a 7S RNA. It is my understanding that the Alu sequence
was originally derrived from a "renegade" 7S gene, but that it is now
a selfish element, and has nothing to do with 7S expression or function.
The human Alu is actually a tandem dimer, and each Alu bears more
similarity to one another than any do to the 7S sequence.
Also, I believe that you are wrong in your assertion that Alu is not a
retro-element, it has an RNA pol III promoter, and appears to undertake
RNA mediated transposition. If you would like to check up on me, or perhaps
introduce some facts into your arguement, try the chapter on SINEs in
the Mobile DNA book edited by Berg and Howe.
Lastly, I would like to know why you would think that a retro-element
present in the genome 500,000 times is "mysterious", while an
equal number of genes for the 7S RNA is not.
Patrick Keeling
Dept. of Biochemistry,
Dalhousie University,
PKEELING at AC.DAL.CA